1. Field of the Invention
The present invention relates to a non-volatile memory device and a manufacturing method thereof. More particularly, the present invention relates to a variable resistance non-volatile memory device including a variable resistance element which reversibly changes its resistance value in response to an electric pulse applied thereto, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, with progresses of digital technologies, electronic devices such as portable information devices and information home electric appliances have been developed to provide higher functionalities. With achievement of the higher functionalities of these electronic devices, further miniaturization and higher-speeds of semiconductor elements incorporated into these electronic devices have been progressing at a high pace. Among them, use of a high-capacity non-volatile memory, which is represented by a flash memory, has been expanding at a high pace. Furthermore, as a novel non-volatile memory in a next generation which has a potential of replacing this flash memory, a resistive random access memory (ReRAM) incorporating a variable resistance element has been studied and developed.
The variable resistance element refers to an element having a characteristic in which it reversibly changes its resistance state (resistance value) in response to an electric signal and is able to preserve the changed state. By allocating information to respective resistance states of the variable resistance element, the information can be stored in a non-volatile manner. Specifically, for example, “0” is allocated to one of a low-resistance state in which a resistance value is relatively small and a high-resistance state in which its resistance value is greater than the resistance value corresponding to the low-resistance state, and “1” is allocated to the other of these resistance states, binary information can be stored.
The conventional variable resistance element is configured to include, for example, a variable resistance layer disposed between a first electrode and a second electrode, the variable resistance layer comprising two variable resistance materials which are different in degree of oxygen deficiency from each other and stacked together. By applying an electric pulse (e.g., voltage pulse) between the first electrode and the second electrode of the variable resistance element, the resistance state is changed from the high-resistance state to the low-resistance state or from the low-resistance state to the high-resistance state.
In the variable resistance memory, it is desired that the low-resistance state and the high-resistance state corresponding to the binary information be clearly distinguished from each other, and switching between the low-resistance state and the high-resistance state take place stably and at a high speed.
International Publication No. 2008/149484 discloses a non-volatile memory element which includes a first electrode, a second electrode and a variable resistance layer which is interposed between the first electrode and the second electrode and reversibly changes its resistance value in response to electric signals which are applied between these electrodes and are different in polarity from each other, the variable resistance layer including in a thickness direction thereof a first region comprising a first oxygen-deficient tantalum oxide having a composition expressed as TaOx (0<x<2.5) and a second region comprising a second oxygen-deficient tantalum oxide having a composition expressed as TaOy (x<y<2.5).
International Publication No. 2012/073503 discloses a non-volatile memory element which includes a first metal wire, a plug formed on and above the first metal wire and connected to the first metal wire, a stacked-layer structure which includes a first electrode, a second electrode and a variable resistance layer and is formed on and above the plug such that the first electrode is connected to the plug, a second metal wire formed on and above the stacked-layer structure such that the second metal wire is directly connected to the second electrode, and a side wall protective layer which covers a side wall of the stacked-layer structure and has an insulativity and an oxygen barrier capability, a portion of a lower surface of the second metal wire being located below an upper surface of the stacked-layer structure.